Isolated Antiphospholipid Syndrome Nephropathy (aPL Nephropathy)—A Rare Cause of a Rapid Decline in Kidney Function in a Patient With Systemic Lupus Erhythematosus

Lupus nephritis (LN) is one of the most common renal manifestations of systemic lupus erythematosus (SLE). However, conditions other than LN can result in a rapid decline in kidney function. We present a clinical case of a young patient with SLE who developed arterial hypertension, arthralgia and morning stiffness in knee and hand joints, an increase in serum creatinine levels from 194 to 532 mol/L, proteinuria of 1.65 g/L and thrombocytopenia of 1000/μL. Kidney biopsy showed isolated antiphospholipid antibody nephropathy (aPL‐N) without any signs of proliferative LN or tubulointerstitial nephritis. The patient was treated with low‐molecular‐weight heparin, followed by warfarin (target INR 2.0–3.0), low‐dose glucocorticoids and azathioprine, resulting in SLE remission and partial recovery of kidney function. This study demonstrates that isolated aPL‐N can cause a rapid decline in kidney function in patients with SLE. To avoid diagnostic errors, kidney biopsy should be performed in a timely manner in all patients with SLE according to standard indications.